1. Field of the Invention
The present invention relates to a board inspection apparatus for inspection of condition of solder that has been printed or the like on a printed board.
2. Background Art
Generally, a printed board is equipped with an electrode pattern on a base board formed from glass epoxy resin, and the surface of the printed board is protected by a resist film. When electronic components are mounted on the above mentioned printed board, firstly, cream solder is printed at certain positions on the electrode pattern that are not protected by resist film. Thereafter, the electronic components are temporarily fixed to the printed board by use of viscosity of the cream solder. The above-mentioned printed board is conveyed to a reflow furnace, the printed board is subjected to a certain reflow step, and soldering is performed. In recent years, the printed condition of the cream solder has been inspected at a stage prior the printed board being conveyed to the reflow furnace. During this inspection, a pass-fail determination is made of the printed condition of the solder based on height or the like of the cream solder as measured by a three-dimensional measurement apparatus.
For example, a three-dimensional measurement apparatus that uses the phase shift method uses an irradiation means to irradiate on an object (i.e., the printed board in this case) an optical pattern having a striped light intensity distribution using visible light as the light source. Then, the object is imaged by a CCD camera, and by analysis of the phase differences of the fringes of the above mentioned optical pattern based on the obtained image, three-dimensional shape, and especially height, of the cream solder or the like is measured.
Then, a pass-fail determination is made for the solder based on the volume or the like of the solder calculated taking average height of the resist as a standard height (e.g., see Patent Document 1), or a pass-fail determination is made for the solder based on height of the solder calculated taking height of the surface of the resist as a standard height (e.g., see Patent Document 2).
Patent Document 1: Japanese Unexamined Laid-open Patent Application No. 2002-228597
Patent Document 2: Japanese Unexamined Laid-open Patent Application No. 2005-140584.
However, when the solder is inspected based on average height of the resist film, it is possible that defective solder may be determined as passing due to an inability to sufficiently ensure actual bonding ability with the electronic components despite there being a sufficient amount of solder protruding from the standard position (i.e., average height position).
For example, as shown in FIG. 9(a), among multiple solders 82a through 82f on a printed board and existing in the mounting area of a certain electronic component 80, solders 82a and 82f may exist in regions where the surface height 83a of the resin film 83 is high. Thus, the amount of protrusion of the above mentioned solders 82a and 82f from the peripheral resist film 83 is insufficient, and when the electronic component 80 is actually mounted, the amount that the solder is pressed down by the various electrodes (referred to below as the crush amount) becomes small. A printed board that should normally be determined to have failed due to inadequate connections, may be mistakenly determined to be a non-defective because there was a sufficient amount of protrusion from the average height position Kx of the resist film 83.
In a similar manner, when inspection of this solder is performed using height of the resist film at the periphery of the solder as the standard height, despite there being a sufficient amount of protrusion from the standard position (i.e., surface height position of the resist film), a printed board may be mistaken determined as non-defective even though actual bonding to electronic components can not be sufficiently secured.
For example, as shown in FIG. 9(b), among multiple solders 92a through 92f on a printed board 91 and existing in the mounting area of a certain electronic component 90, solders 92c and 92d may be present in a region of low surface height 93a of the resist film 93. During lowering of the electronic component 90 onto the printed board 91 for mounting, the electronic component 90 contacts the high positions of surface height 93a of the resist film 93 (see the dashed-to-dotted line image of FIG. 9(b)), and the electronic component 90 does not approach the printed board 91 any further. As a result, the crush amounts of the solders 92c and 92d become low, and thus a printed board that should normally be determined to be defective due to inadequate bonding, may be mistakenly determined to be a non-defective since there was a sufficient amount of protrusion from the surface height 93a of the resist film 93.
The above described failures can similarly occur even when co-planarity is inspected.